Mobile Website Speed Test

Why mobile speed is the only speed that matters

Since 2019, Google has used mobile-first indexing — your mobile site is the primary version Google crawls and ranks. Even when someone searches from a desktop, Google's ranking decision is mostly based on your mobile experience.

That makes mobile speed not just a performance concern but an SEO concern.

The numbers are brutal:

• 53% of mobile visitors abandon a page that takes longer than 3 seconds to load (Google)
• A 1-second improvement in mobile load time can increase conversions by up to 27% (Deloitte)
• Sites that meet Core Web Vitals thresholds see 24% fewer abandonments (Google)

What Lighthouse mobile testing simulates

When you run a mobile speed test, Lighthouse applies three throttles:

1. CPU throttling: 4× slowdown — to simulate a mid-range Android
2. Network throttling: slow 4G — 1.6 Mbps down, 150ms RTT
3. Mobile viewport — 360 × 640 pixels

That's intentionally pessimistic. It represents your real user, not a developer on fiber with an M-series MacBook.

The biggest mobile-specific killers

1. Massive JavaScript bundles

JS that runs fast on a laptop can stall a phone's main thread for hundreds of milliseconds. Code-split your bundles, defer non-critical scripts, and prune unused dependencies.

2. Huge images

A 2MB hero image will tank your mobile LCP. Always:

• Serve responsive images with srcset and sizes
• Use modern formats (AVIF, WebP)
• Lazy-load anything below the fold
• Compress aggressively (TinyPNG, Squoosh)

3. Third-party scripts

Every analytics tag, chat widget, A/B test, and ad pixel taxes the main thread. On a slow phone, those costs explode. Audit your third parties ruthlessly and defer everything that isn't visible above the fold.

4. Web fonts

Custom fonts cause Flash of Invisible Text (FOIT) or layout shifts (CLS). Use font-display: swap, preload your most important font weight, and consider self-hosting instead of pulling from Google Fonts.

5. Tap target size

A subtle one: if your buttons are smaller than 48 × 48px or too close together, Lighthouse will flag it under both Accessibility and Best Practices. Bigger tap targets = happier mobile users.

How to interpret your mobile result

Don't compare directly against desktop. Mobile is harder. Reasonable benchmarks:

• 90+ — Elite. You're in the top 5% of mobile sites.
• 70-89 — Good. Most well-built sites land here.
• 50-69 — Needs work. Likely JS or image-heavy.
• Below 50 — Painful. Users are leaving before your page loads.

Run a mobile test on your site below and we'll show you exactly what to fix first.